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package org.example.jdbc;
import java.sql.*;
public class FirstExample {
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=CTT";
    static final String USER = "root";
    static final String PASS = "jianan";
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            // 加载数据库驱动
            Class.forName(JDBC_DRIVER);
            // 连接数据库
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            // 执行SQL查询
            stmt = conn.createStatement();
            String sql = "SELECT id, age, first, last FROM Employees";
            rs = stmt.executeQuery(sql);
            // 遍历结果集
            while (rs.next()) {
                int id = rs.getInt("id");
                int age = rs.getInt("age");
                String first = rs.getString("first");
                String last = rs.getString("last");
                System.out.printf("%d,%d,%s,%s", id, age, first, last);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 释放数据库资源
            try {
                if (rs != null) {
                    rs.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try {
                if (stmt != null) {
                    stmt.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try {
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

注：该代码已被优化，主要改动包括：

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